Fluid-Structure Interaction
by DamWaters
Summary: When Percy and Annabeth meet in their senior year of college, the connection is immediate and undeniable. With graduation just around the corner and uncertainty following close behind it, will they be able to build something permanent, or go their separate ways? - A Percabeth College AU set at my own university; rating for language and potential future content
1. Interdisciplinary

Chapter 1: Interdisciplinary

* * *

It had rained every Tuesday this semester. Normally he wouldn't have minded, but Percy Jackson had a half-mile between classes on Tuesdays, and even the best swimmers got tired of being wet. Why his bio lab had to be so damn far from his Greek class, he couldn't fathom. He supposed he could just take the bus. Being on a large campus had its perks, but he had vowed during his freshman year never to use the free transportation unless he was gravely injured. So, rain, sleet, or snow, Percy could be found walking to class.

The cloying smell of formaldehyde greeted Percy like a mortician as he reached his destination and opened the door. The ventilation system in this building was probably hazardous, but since the school had just spent a crazy amount of money on the new design building, engineering center, and business school expansion, a small project to fix it was just wishful thinking. Those projects were pretty amazing though, Percy thought. His school wouldn't be ranked the ugliest college campus next year, for sure.

Percy took his usual seat next to his friend Grover, who he had known since middle school. Grover wanted to "save the natural world from the violent destructive forces of capitalism," so he took many of the same courses as Percy, who hoped to be a marine biologist. Their interests had been shaped by their friendship, and they could often be found together at environmental rallies and protests, among the most vocal participants. They even had their own shirts made specially for those events. Grover's said "save the motherfuckin' bees" and Percy's said "save the motherfuckin' whales." Percy's ex-girlfriend Rachel had done the artwork below the words.

Today's lab work was another dissection, which Grover found offensive and despicable, and which Percy found engaging and interesting, though he didn't voice these opinions to his friend. The recent lecture portion of the class had focused on a new concept called fluid-structure interaction, the idea that biological and man-made structures interact in predictable ways with internal and external forces to reduce strain and generate thrust. It was making its way into mainstream science (was that a pun?) and specifically interested Percy since he studied the interaction between forces in marine ecosystems. The simple act of swimming was in fact an example of this concept.

A lot of people thought that Percy was unintelligent, since he received accommodations in classes for his learning disabilities. The opposite would be more accurate. Percy Jackson was a genius, if you looked past IQ scores and homework grades. He lived and breathed water. Some said he did so literally, looking at his record-breaking swimming career. He could tell you more about the intellect of octopuses than he could about that of humans. Personally, he thought octopuses might have the edge in any real battle of wits. More importantly, he could make other people understand the importance of marine ecology in their own lives and stir passions in the most stoic audiences. He had a gift, really, even if he himself didn't know it.

An hour and a half later, Percy and Grover disposed of the separated fish bits and left to find fresh air.

"Hey, Percy!"

Percy turned just in time to be knocked on his ass by his ex-girlfriend and current friend. Some people would have found their relationship strange, or thought the friendship to be a cover for something less innocent, but Percy didn't care. Rachel had been a good friend before the dating disaster, and would be a good friend after too.

"Hey, Red."

"Guess what today is!"

"Umm... Tuesday?"

"No, you idiot... well, yes technically, but that's not the point. Today is Senior Success."

Percy groaned. He had forgotten about that entirely. Rachel was a member of the student government and she was putting on some sort of networking event just for current seniors to meet their peers from other majors. She claimed it fostered "interdisciplinary cooperation," whatever that meant. Since Rachel's father was the largest single donor to the university, it was never really a question of whether she would get her way. Most professors had been cajoled into requiring attendance, which was sure to set the student enthusiasm level at zero, maximum. The only person who seemed at all excited was Rachel herself, and she was happily ignoring the irritation surrounding her.

"Oh, yay."

Rachel rolled her eyes, very aware of Percy's thoughts on the matter. She grinned impishly.

"It's business attire, so if you show up in sweats and ruin this for me I swear to the gods I'll kill you, okay hun?" Her false cheer sent shivers down Percy's spine. He was not a fan of that voice, and he knew Rachel was serious enough not to risk arguing. He might not end up dead, but an angry Red was not a pleasant experience.

"Sure thing. I'll dig out my best."

"Good. And take a shower Percy, you smell like death."

Rachel Elizabeth Dare waved goodbye, off to track down her next victim.

Grover muttered under his breath, having been completely ignored.

"You know, she might talk to you again if you apologize for calling her father an environmental terrorist."

Grover scoffed.

"Just a thought."

* * *

The new design building was nice, she had decided, but the constant rain during her Tuesday afternoon classes prevented her from enjoying the abundant natural light that made the building truly impressive. Annabeth Chase was still unused to the cold rain of New England, having grown up in California with her father, step-mother, and two half-brothers. She hadn't realized the truth behind the phrase "chilled to the bone" until she transferred here. Her friend Connor hadn't mentioned the biting wind and sub-zero temperatures in his letters raving about the architecture program here. She should have known better. Still, the professors were helpful and Connor was her TA, so she was happy with her choice of school. Her friends back home joked that she only moved east to be two thousand miles closer to Greece. They weren't exactly wrong, since she was making plans to go after graduation, still almost seven months away.

Greece had been her muse for as long as she could remember. Fredrick Chase, Annabeth's father, was a Combat History professor at UC Berkley. When Annabeth was young, he often would say that her mother had been as beautiful and smart as Athena herself, and that one day Annabeth would build something to rival the greatest temples of Athens. Those little moments they shared fell away when her father's favorite former student, Elizabeth, became a regular guest in their home after graduating, and a regular guest in his bed not long after. Annabeth was ten at the time. Even without her father's assurances, Annabeth still felt drawn to Greece, to its culture, its history, and most of all its architecture. Almost every single one of her designs incorporated columns or richly decorated pediments.

Unfortunately, not every project allowed for her typical hellenistic input. Today, for example, was another round of engineering theory, aimed at improving students' grasp of an intrinsically linked field of study. They would be incorporating moving parts to their models, based on the Fluid-Structure Interaction theory. Examples of this theory in action included the seismic-dampening properties of traditional Japanese structures using the "ishibadate" system of supports instead of fixed posts. While Annabeth found it interesting, she has no idea how she was going to create a new design based on these new principles. She would just have to come up with something, in the end. Architecture was her passion and her gift, even if she didn't know it.

"Hey, Annie."

Annabeth's eye twitched at the sound of her newest friend's voice, and more specifically at the name she hated. She had met Rachel Dare early this year, after attending a career event sponsored by her father's real estate business. Well, more like real estate empire, really. Dare Enterprises owned and operated a private architecture firm which designed only the biggest and most important projects. The building she currently occupied was one such project. Yet another gift to the university. It was Annabeth's dream job to work in such a high profile company. The pay would be nice too. She put down her pencil and turned to face the redheaded interloper.

"Hey, Rachel."

"Are you ready for tonight? I've been asking everyone I know to stop myself from freaking out."

"You do realize most of us have no choice, right?"

"Doesn't stop me from worrying. I just want this to go well. I want to prove that I can be successful on my own."

Annabeth's gaze softened. One of the things she had in common with Rachel was a thirst to prove herself to her father. Annabeth was working to earn her father's praises again, but Rachel was still waiting to be noticed.

"I'm sure it will be brilliant. Let's just hope the business majors can keep their egos in their pants."

"Don't count on it. I'm sure you'll meet at least one interesting person though. I'll introduce you to a friend of mine who promised to be there. Then you can at least be miserable together while I mingle."

Annabeth rolled her eyes. "How kind of you."

"I do try. Now get out of here and get dressed. You look like a bum."

Annabeth just grinned at her friend as Rachel waved a goodbye.

Rachel left with a grin of her own, her thoughts on the one connection this networking event was really meant to make. Sometimes subtlety was overrated.

* * *

"I'm glad you made it."

"I recall being threatened with death if I didn't"

"Oh gods, that's awful. Who would do such a thing?" Rachel asked innocently. She started looking around.

"Looking for someone?"

"Two someones actually. Where's your... friend?"

"Grover is protesting. I convinced him to at least protest silently, at the apartment."

"Thanks for that, I guess."

Percy shrugged. "Who is the second someone?"

"A girl named Annabeth. She's a transfer student from Cali."

"She transferred her senior year?" Percy asked, one eyebrow quirked in surprise.

"Yeah. She says she heard about the architecture program from a friend."

"Huh." Percy was from out of state too, but California was a lot further than New York.

"There she is!" Rachel waved to get her friend's attention.

Percy followed her gaze... and took a sharp breath in. This Annabeth girl was _beautiful._ Who knew a pantsuit could look so good? Rachel was watching his face, and grinned like a cat that caught the canary. It was a little bittersweet. She remembered when he looked at _her_ like that, but they really were better as friends than lovers. She hoped her two friends could be good at both.

"Hey, Annabeth."

"Hey yourself. This is amazing, Rachel." It was no idle compliment. The event was being held at the football field to accommodate the large number of students, and quite frankly there had never been this many people present for an actual game. Football in New England didn't matter unless you were the Patriots. Right now the stadium was lit by yellow string lights rather than the harsh stadium lights, giving the whole field a soft glow. The turf itself was covered in interlocking vinyl planks painted to look like hardwood.

"Thanks, Annie." Percy noted her grimace. "Have you met my friend Percy?"

Annabeth looked up to meet his gaze, eyes widening for a moment before she looked back to a smirking Rachel. "I'm afraid not."

"Well now you have. Percy, take good care of her for me, will you? Converse, socialize. I'll be back later."

Rachel left them facing each other awkwardly as she made a beeline for he far side of the stadium.

"So... Red tells me you're an architect."

"Red? You mean Rachel-"

"Elizabeth Dare, yeah. It's her nickname from way back when. 'Cause it comes from her initials and also because she has... red hair," he finished, trailing off in embarrassment.

"You two must be close then."

"We are. She's one of my best friends."

Annabeth sensed there was more to the story, but since she had only just met Percy, she let it slide.

"That's great then. She's been great to me since I transferred. Really the only one our age who I talk to. I hardly ever leave the studio."

"Probably why she organized this event then. I had wondered."

"What do you mean?"

"Red never does anything halfway. If she wanted a new friend to meet people, it's exactly like her to get the entire class involved."

"So all this is for... me?" Annabeth found the idea absurd. She wasn't even that close to Rachel, and certainly not worth the hassle that must have gone into planning this whole event.

Percy's eyes locked on her own, and she felt his stare like a physical force. The sea green eyes cashing into her like the waves. He took a step forward.

"She does a lot for her friends, but this is big even for her, I admit." He paused and added softly, "you must be worth it." His eyes never left Annabeth's and she felt her face warm dramatically at the sincerity in his voice. She took a step forward.

Percy looked away slowly, a blush growing on his own face as he noticed the shrinking space between them for the first time. The networking night had only just begun, but the desired connection had already been made.

* * *

**AN:** _Well here we go. My muse disappeared for my other stories, so I'm looking for her in the Percy Jackson Fandom. Sometimes a change is what it takes to get the creative juices pumping. I debated writing this entire story before publishing, but decided against it. This will grow into something more, I hope, and give me another outlet for when my other stories slow down. I hope you enjoyed this first chapter._

_Cheers,_

_DamWaters_


	2. A History Lesson

**Chapter 2: A History Lesson**

* * *

Grover noticed the bounce in Percy's step as he made his way into the apartment. He had been waiting the entire evening, protesting the forced participation in what he deemed an irresponsible waste of time and resources.

"Looks like someone had a nice evening," he commented drily.

Percy quirked an eyebrow at his friend's tone. "Was it you, Grover? That would be strange, since all of our friends were at the event, but it looks like you had a wild night." Percy gestured jokingly to the immaculately clean apartment. His mood wouldn't be diminished by a surly roommate, that was certain.

"Okay, aqua man, what the hell is up with you? You look like the Stoll brothers twenty minutes after they share a joint."

"I met someone tonight."

"Well that explains it. A girl, I'm guessing? Weren't you supposed to be going with Rachel?"

"No. I was going _for_ her. And anyway, Rachel is the one who introduced us."

Percy had his friend's attention now. Grover turned to face him fully, surprise evident on his face.

"Why?"

"I don't really know. Guess she's really moved on... and thought I should too."

Percy was filled with the same bittersweet memories that had struck the girl in question earlier. He missed the days with Rachel, and the one summer they shared as a couple. They were always going to share something special, but some part of Percy was proud of her for choosing to move forward. She deserved it. And now, he realized that he did too. Percy hadn't dated since the breakup, convincing himself he was perfectly happy on his own. He truly had been for a while, but now, after tonight, he was beginning to realize he could do better.

Grover grunted an acknowledgement. "Well good for you then. You could do better than that devil-spawn."

"She's not her father!" Percy jumped to Rachel's defense, for the hundredth time at least.

"Whatever. She hasn't done anything he wouldn't do, besides date an ecologist, I guess."

"What do you have against her? Why the hell can't you let her be her own person?"

"You're only defending her because you fucked her, so you can - "

"Shut up." Percy growled, his eyes narrowing. "Shut up right _the fuck_ now."

Grover hesitated, thinking perhaps he had gone too far this time. Percy's tone had his alarm bells ringing loudly. He raised his hands in surrender and waited.

Percy's gaze never softened. "I'm getting out of here. I was having a good night before you decided to be an asshole."

"I... well... sorry, man."

Percy shook his head in frustration, sighing quietly. "I'm not the one you need to apologize to." With that, he turned and walked out the door, leaving Grover alone with his thoughts in the dark apartment.

* * *

On the other side of campus, another pair of friends made their way up a flight of stairs to a large private suite.

"Wow, Rachel, this place is amazing. Thanks for the invite."

"Any time, Annie. I'm glad you decided to take the night off for once."

"I'm not sure I could focus on work right now, honestly. You did a brilliant job tonight. I think most people were pleasantly surprised."

"I just thought we could all use a night to feel good about ourselves, you know? A glimpse into a brighter future."

Annabeth nodded. "Hey, Rachel?"

"Yeah?"

"Can I ask you a question? It's about your friend Percy."

Rachel smiled nervously, wondering if she had already been found out for her scheming. "Of course," she murmured.

"Is there something going on with you two?"

Instead of answering immediately, Rachel looked at the clock on her microwave. It was quarter past eleven, much too late for a full explanation, so she went with the Spark Notes version. She led Annabeth to the stools at the kitchen counter.

"Sit, and I'll explain." She gathered her thoughts as her friend followed her instruction.

"Percy and I became friends the summer before high school. It's a very long story, but let's just say he got into some trouble and I helped him out. After that, he and I were inseparable, though one of his friends, Grover, made a big fuss when he found out about my dad. Grover is an environmentalist, like Percy, but he takes it way too far sometimes." She scowled at some of the more recent memories. "Anyway, after high school, I took a chance to see if Percy and I could be more than friends. We lasted all of three months before it fell apart, even though we both loved each other, and were pretty open about our feelings. What we have now is sort of complicated, but we're just friends, really. We work better that way. I know we'll always be close, and some people think that's bad, but he's important to me, so they can fuck off."

Annabeth could tell the redhead had more to say, so she let Rachel finish, despite getting her answer already.

"It's been years now, and I think we're ready to move on, so I'm giving both of us a chance. He has so much to offer, and I want him to be happy, ya know? Even if it won't be with me." She finished with a weak smile before the floodgates opened and she began to sob loudly into the shoulder of a somewhat startled Annabeth.

"Whoa, Rach, it's okay."

"I'm s-sorry. It just... it hurts a little, knowing what could have been."

Annabeth felt guilty for causing this reaction from her friend, even if it was only an accident. "Why haven't you tried again? If there's still something there, it could be worth it."

"There's not enough." Rachel took a deep breath to steady herself and wiped her eyes, erasing her moment of vulnerability. "Trust me, I used to think the same thing, and he knows that. We talked it through like adults and decided to just be friends. Tonight just sort of sealed the deal."

"What do you mean?"

"I saw the way he looked at you, Annie. It's the same look he used to give me whenever I dressed up for events or took him to the beach. He gets this expression like he just got handed blue cookies. Surprised, and then happy as hell. I haven't seen him look like that at anyone else till tonight."

Annabeth didn't meet her friends gaze. "I'm not going to steal your boyfriend, Rachel."

Rachel rolled her eyes at her friend's obliviousness and poorly disguised disappointment.

"For someone so smart, you're being super dumb about this, Annie. I want you to steal him. In fact, I'm giving you permission to go for it. I think he can make you happy, and you can make him happy too. And seeing my friends happy is all I'm hoping for here."

Percy's comment from earlier was starting to seem like an actual possibility, albeit slightly skewed. "Umm... Rachel? You didn't, by any chance, set this event up _just_ to introduce us, did you?"

Rachel blushed slightly, giving Annabeth all the answer she needed.

"Oh my gods! Seriously, Rachel?" she shouted. "I thought Percy was joking about that. What if we had hated each other?" Her eyes widened in confusion. "You've been planning this thing since September! You didn't really even know me then. How could you possibly think that I would be a good match for your ex-boyfriend, as ridiculous as that whole idea is anyway?"

Rachel huffed defensively. "I know Percy better than he knows himself sometimes. I knew he would like you about a week after I met you. The first time we really got to know each other. Do you remember that day, Annie? You were so eager to make a new friend that you were making _me_ nervous just watching you. And then you talked about how you were already in love with the program here, and how you really thought you could make something of yourself. It was sweet, really, how you forgot we were still practically strangers when you got into it." Rachel smiled fondly at her best friend. "I met Percy for dinner that same day. Wanna know what he said? He said he was already in love with his new classes and he really felt like he was finally going to learn the things he wanted to, and be able to make something of himself. You both had such passion about your future that I knew right then that you two had to meet. And I knew that without me, you probably never would. What were the odds you would even notice each other with so many people around? Clearly, it worked out in the end. Don't think I didn't notice the look on your face when you saw him tonight. That was adorable, by the way," she finished with a sly grin.

"Adorable or not, why would you go through all that for him?"

"Not just him, little Annie. I did it for you too. I know it's weird, with my history with him and everything, but you have to follow your heart on this one, and forget about that. I want this to work out for you guys. I really, really do. Please, just give it a - "

A sound of a sonar cut her off. There was only one person with that ringtone. Percy was calling.

Rachel answered somewhat nervously.

"Are you free, Red?" His gruff tone told her immediately that something was wrong.

"Sort of... whats the matter Percy?"

"Nothing. I just can't be at the apartment right now with that idiot."

"Grover? What did he do now?"

There was a pause, which of course meant he was deciding what to tell her.

"It doesn't really matter. Just something about... us."

"Oh." She looked over at Annabeth, who had sensed something was up and covered her ears, pointedly looking anywhere but at Rachel.

"Yeah. So can I come over? Just so I can cool off a bit? I don't want to ruin your night, so if you want I can hang at the library instead."

"It's no problem. Sorry about Grover. I didn't mean to set him off."

"Oh I know. There's just something about you," came the reply. She could almost see his crooked grin. "I'll be there in five. The buses are still running."

"Okay. See you soon."

She hung up and banged her head on her counter.

"He's coming?" Annabeth asked nervously.

She nodded.

"Should I..."

"No. Stay. It's no big deal. His roommate is just being an ass again."

Annabeth nodded, fitfully running her hands through her hair, noting anxiously how tangled her curls had gotten, before her attention shifted to her wrinkled blouse. Her breathing sped up as she mentally catalogued her appearance. She was far less confident now that she had a chance to worry about seeing Percy again.

Rachel looked over to see her friend on the verge of a panic attack. While it spoke volumes about her talent for matchmaking, Annabeth passing out would be really inconvenient at the moment.

"The bathroom is just down the hall if you need a minute, Annie."

The blonde made her escape like a frightened animal, barely pausing to fetch a comb and toothbrush from her duffel bag. Rachel chuckled quietly. Now to wait for Percy's reaction to her gorgeous guest. She sat at the counter and counted down the minutes.

* * *

For reasons best kept secret, Rachel had given Percy a key to her apartment. Thus, the two young women inside were given no warning before he entered.

"Hey, Red! Where are you?"

Rachel called back from the kitchen. "In here!"

Percy made his way toward her, not noticing the floral-patterned bag in the living room, or the small squeak of surprise as he passed the bathroom in the hallway.

"Hey. Sorry to barge in on you like this. I just couldn't handle Grover's shit after tonight. You did awesome with that by the way. I heard more compliments than criticisms, so you either did something right or spiked all the punch bowls. Apparently you managed to please everyone but my roommate with this little stunt of yours."

"Speaking of which. What's the furball's problem this time? I wasn't even there to piss him off properly."

"I think he was just annoyed that I took your side and went tonight. He got pretty nasty again when I got home. I was having a nice night before that, so I peaced out before he could get going."

"I'm surprised you enjoyed such a formal event. It's not usually your style. Was there any particular reason you enjoyed your evening? A new friend, maybe?"

Percy rolled his eyes. "You know you're really terrible at being subtle, right? I would almost feel bad for you, but... thanks, Red. Are we still cool?"

"Yeah." She grinned as Annabeth came in just behind Percy, too quietly for him to notice. She caught her friend's eye and conveyed the need for silence. "Only if you spill the deets on what I missed between you and Annie. What are your intentions toward my friend, mister?"

Percy ran his hands through his hair, unknowingly mirroring Annabeth's own nervous tic. "I don't know. She's brilliant, obviously. I'm not sure I could keep up with her there. And she's... well, breathtaking is the only word for it really." He leaned back and his voice dropped to a whisper so low that only Annabeth could hear him. "I just don't want to screw that up a second time."

"Well if she's brilliant and breathtaking, why don't you ask her out?"

Percy laughed. "Just like that?"

"You wont know till you try." Her gaze passed over something behind Percy and he tensed.

"She's right behind me isn't she?

Rachel cackled madly and nodded.

"And she heard all of that?"

A voice like music answered softly.

"Yeah, I did."

The redhead smirked "How's that for subtle, Percy?"

* * *

A/N: And here we are with chapter two. Who knows how many we have left? Not me, that's for sure. Enjoy, review, fav, or follow. I beseech the opinions and affections of my audience.

Cheers,

DamWaters


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